1. Field of the Invention
The present invention relates to an optical signal processing apparatus which multiplexes or demultiplexes signal light with multiple wavelengths.
2. Related Background Art
A diffraction grating element acts as a so-called wavelength branch means. When multiplexed signal light with multiple wavelengths is input to a diffraction grating element, the signal light with multiple wavelengths can be branched into the respective wavelengths. An optical signal processing apparatus using such a wavelength branch means can receive multiplexed signal light with multiple wavelengths, demultiplex it into signal light components of the respective wavelengths or bands, and output the signal light components. Alternatively, the optical signal processing apparatus can multiplex signal light components with multiple wavelengths, which are input for the respective wavelengths or bands, and output multiplexed signal light. The optical signal processing apparatus is used as an optical multiplexer or optical demultiplexer in an optical communication system.
For example, in an optical signal processing apparatus disclosed in Japanese Patent Laid-Open No. 6-300937, multiplexed signal light with multiple wavelengths is made incident on a diffraction grating element, the signal light is wavelength-branched using a fact that the light diffraction angle at the diffraction grating element changes depending on the wavelength, and the wavelength-branched signal light components of the respective wavelengths are output to spatially different optical paths. Of these wavelength-branched signal light components, a signal light component having a specific wavelength is separated from the remaining signal light components which have wavelengths other than the specific wavelength by arranging a reflecting mirror on the optical path of the signal light component with the specific wavelength. In this way, the optical signal processing apparatus can operate as an optical demultiplexer. When light travels in a reverse direction, the optical signal processing apparatus can be used as an optical multiplexer. In the optical signal processing apparatus disclosed in the above prior art, movable reflecting mirrors are arranged in the optical paths of the wavelength-branched signal light components with multiple wavelengths. A reflecting mirror is placed on the optical path of the signal light component having a specific wavelength to be separated while the reflecting mirrors are removed from the optical paths of the remaining signal light components which have wavelengths other than the specific wavelength. With this arrangement, the wavelength of signal light to be demultiplexed or multiplexed is changed.